The invention relates to methods of performing oil and gas production in deep-sea areas with hard hydrometeorological and climatic conditions and to a construction of marine hydraulic engineering structures, in particular, to deep-sea platforms.
Known in the art is a relevant method of oil and gas recovery in deep-sea areas of the ocean with hard hydrometeorological and climatic conditions including performance of such a job from a platform provided with all necessary basic and auxiliary equipment, including energy and life support devices with the respective building structures and constructions (cf. Mirzoev D. A. xe2x80x9cSpecific features of design and technology for development of the Arctic oil fieldsxe2x80x9d, xe2x80x9cHydraulic Engineeringxe2x80x9d, 1994, 1994, No. 3, pp. 24-29).
Also known in the art are devices such as a deep-sea platform including an upper structure, a support part and a foundation, basic and auxiliary equipment required for performing oil and gas recovery, energy and life support with respective building structures and mechanisms (cf. Mirzoev D. A. xe2x80x9cSpecific features of design and technology for development of the Arctic oil fieldsxe2x80x9d, xe2x80x9cHydraulic Engineeringxe2x80x9d, 1994, 1994, No. 3, pp. 24-29).
The disadvantages of the known methods and devices for deep-sea shelf areas of the ocean with hard hydrometeorological and climatic conditions (including the Arctic shelf areas) is a necessity of withstanding significant static and dynamic loads with a large load arm and, as a consequence, a large volume of building materials used for heavy-duty robust support structures and foundations, and high labor consumption for performing all building and assembly jobs and prospecting. As for buoyant platforms, the work must be ceased at a high wind and waves, there is a danger of tumbling during icing, adverse working conditions for the people, equipment, building structures and mechanisms. As a result, the cost of building the structures and performing the oil and gas recovery is high.
An object of the present invention is to change the conditions of execution of oil and gas recovery allowing one to avoid the affects of the ice, storm and other loads on the offshore oil and gas production platforms and the associated facilities, to substantially reduce the scope of the building and assembly works and engineering prospecting, as well as to reduce the material and labors cost when building the foundations and support structures, to improve the operating conditions of the personnel, equipment, building structures and structural members, to increase safety of the personnel, reliability of the structures and protection of the environment at primary and emergency blowouts of hydrocarbons and in other emergency situations thus considerably reducing the platform cost, labor cost and time needed of its erection, to expand the area of the oil and gas fields serviced by the platform, to increase the platform mobility with a possibility of its transfer both over the oil field area and in other areas, and to considerably expand the range of oil and gas recovery area on the shelf and adjacent zones of the ocean including the Arctic Zone.
This object is attained by providing a method for carrying out operations on oil and gas fields in deep-sea areas of the ocean with hard climatic and hydrometeorological conditions performed from a platform, provided with all necessary basic and auxiliary equipment including energy and life support systems with respective building structures and facilities. The operations are carried out from a platform, which is located underwater at a depth where it is not subjected to the effect of storm waves or below the undersurface of an ice field. In the process of oil production the platform is supported by a surface complex moving on the water or ice field surface at a speed of the water current or ice drift in an opposite direction, or by a ground-based stationary complex with communication means with the platform and outside world, as well as a set of evacuation and other life saving equipment, as well equipment and instruments for remote control of the production processes on the platform.
With respect to the platform construction, the object of the invention is attained due to the fact that the deep-sea platform includes basic and auxiliary equipment required for performing oil and gas production, energy and life support with the respective building structures and facilities. The platform is made as a closed construction with positive buoyancy water-tight and gas-tight from above and from all sides with an inner space accommodating all equipment, structures and units with ballast compartments and an open drilling well passing through the bottom of the platform with devices for maintaining the necessary air pressure or respiratory mixture and other working gases in the inner space. The walls of the platform are designed for emergency pressure and temperature: they are three-layer with a load-carrying external shell, an internal shell divided into sections interconnected through dowels, and intermediate space between the shells filled with pads of a strong elastic material filled by fluid or gas under a necessary pressure.
The proposed platform may be furnished with floating air inlets controlled from the platform to be placed in preliminarily prepared in ice lane and stacked in non-working state on the platform deck.
The proposed platform can be furnished with underwater reservoirs secured to it from outside and having a shell made of a strong water-tight and a gas-tight material having high thermal conductivity with an outlet in the bottom provided with a cleaning filter, said reservoirs being previously filled with air or inert gas and communicating through pipe lines with a head of a drilling string. Mounted at the end of the pipeline in the inner space of the shell is a burner controlled from the platform, which is fed with oxygen through an additional pipeline.
The proposed platform may be furnished with underwater reservoirs located outside and used for collection of primary or emergency volumes of gas, condensate or oil, said reservoirs being connected to the drilling string head through pipelines. The underwater reservoirs have double shells made of a gas-tight, oil-tight and water-tight material, the external shells being load-carrying and the internal ones being flexible and elastic preliminarily filled with air or water so that an opening is formed in the bottom of reservoirs communicating with the inner space of the internal shell with the environment. The crude oil feed pipelines are arranged in the space between the external and internal shells.
The proposed platform may be also furnished with an end sleeve located at the outlet of the drilling well connected to the platform through a flexible gas-tight, oil-tight and water-tight joint having at its lower end a sliding ring packing preventing pollution of the environment by hydrocarbon crude and the drilling fluid in case of an emergency rise or submergence of the platform. The upper end with the drilling string head moves freely inside the sleeve, and its length is determined by the difference of the marks of the upper end of a string in its extreme working position before building-up of a next link of the string and the bottom of the emerged platform with a correction for its drift with the ice field.
In a proposed platform for the period of a well sinking operation, the drilling string may be provided with a cylindrical collar encompassing the upper part of the drilling string and secured thereon pressure-tight through the upper end under drilling string head and the lower end overlapping the upper end of the casing pipe entering the open oil mine of the platform with a flange freely passing through the shaft and tightly connected with an axially squeezed sleeve made of a strong elastic material, while the lower end is tightly secured on the thrust flange on the casing pipe.
The supports of the proposed platform can be secured in massive support blocks freely lying on the seabed with their macrorough lower surface.
The proposed platform may also be furnished with a reservoir of a respective volume secured to the platform hull and consisting of elastic water-tight and gas-tight material folded in inactive state and filled when necessary, by command from the platform or from the surface complex.
The technical result achieved with the help of this set of features consists in that the oil-and gas-field works in deep-sea shelf areas with hard hydrometeorological and climatic conditions including the Arctic Zone are carried out from a platform arranged in a bulk of water, at a depth not subjected to the effect of storm waves or below the undersurface of an ice field released from the affect of the wave and ice loads, as well as from icing thus removing the uncertainty in the magnitudes, directions and combined actions on the platform during its erection and operation and minimizes them, and also widens the range of oil and gas production on shelf and other zones of the ocean including the Arctic Zone. In so doing the platform is made in the form of a closed structure with an inner space accommodating all equipment, structures and units with energy and life support facilities. In this case the safety of the personnel, equipment and structures when performing oil and gas production is improved, the protection against fire and detonation is provided; the extent of security of production shops and the environment from emergency outbursts of oil, gas, drill fluid and products of incineration of associated gas is increased, the reliability and stability of the platform under unexpected circumstances is improved; and the platform is capable of maneuvering and moving both over the oil field and beyond it.